Along an assembly line, diapers and various types of other disposable absorbent articles may be assembled by adding components to and otherwise modifying advancing, continuous webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. In some configurations, graphics are printed on individual components and/or continuous webs of material used to assemble the absorbent articles. The graphics may be provided by printing ink on substrate materials by various printing methods, such as flexographic printing, rotogravure printing, screen-printing, inkjet printing, and the like.
In some configurations, the printing operations are performed separate to the assembly process, such as for example, printing the substrates offline wherein the printed substrates may be stored until needed for production. For example, printing operations may be accomplished on discrete printing lines, separately from converting lines that are dedicated to manufacturing disposable absorbent articles. After printing on the printing lines, the printed substrates are delivered to the converting lines, such as in a form of continuous webs comprising printed images thereon. However, the above practice of separately printing the substrates offline from the converting lines typically requires additional cost associated with handling, winding and unwinding, storing and shipping of the substrates. In addition, the above steps can negatively affect the quality of the printed substrate, resulting in uneven and often excessive deformations of the wound layers of the substrate inside the roll due to uneven distribution of the compression forces inside the roll. Furthermore, the separately printed substrates often require special registration control methods to ensure proper phasing of the printed images with the converting operations to effect a desired and consistent positioning of the printed image in the produced article.
In an attempt to overcome the aforementioned drawbacks to offline printing, the graphic printing may be done online during the article assembly process. However, combining printing operations with converting operations may create other challenges in performing such printing processes when attempting to maintain aesthetically pleasing final assemblies. For example, contact printing processes, such as flexographic and rotogravure printing processes, may be capable of operating effectively on certain substrates at relatively high production rates. However, such contact printing processes have relatively low degrees of flexibility with regard to the ability to change the design of a printed graphic. When utilizing such contact printing methods, changes in graphic designs would often necessitate the shutdown and restart of the entire converting operation. In contrast, some types of printing processes, such as non-contact inkjet printing processes, may provide more flexibility and ease with regard to the ability to change the design of a printed graphic. In some configurations, a change in graphic design can be implemented by inputting commands to a programmed printhead controller to select a desired image to be printed. However, the use of such commands to periodically change a design may have limited abilities previously not recognized.
For example, it may be desirable to print particular distributions of different images that are not regularly periodic, which is to say, that such distributions would have a degree of randomness to them, and it may also be desirable to weight those distributions according to various factors, e.g. the cost of ink. It may be desirable to provide consumers with packages of absorbent articles having printed substrates bearing a variety of graphic patterns, randomly distributed in such packages. It may be desirable to manufacture absorbent articles having printed substrates bearing coupons or winning tickets a la Willy Wonka. It may be desirable to manufacture absorbent articles having printed substrates bearing a random distribution of graphic patterns: (a) weighted by the cost of ink used per graphic pattern, such that a target cost per manufacturing unit may be achieved; (b) weighted by the volume of ink usage of each color of ink being used, such that, e.g. the ink cartridges (or other reservoirs) of at least two colors are depleted at about or the same time, thus allowing for refilling to be coincident; and/or (c) weighted by drops fired for each printhead, such that, e.g. the useful lifetimes (based on drops fired) of at least two printheads may expire at about or the same time, thus allowing for replacement to be coincident.
It is believed that one or more of the methods and apparatuses for printing particular distributions of different images on advancing substrates disclosed herein may help address one or more of these desires.